1. Field of Invention
The present invention relates to ferrous alloys that possess high-strength, good corrosion resistance in environments such as oilfield exploration, production, and testing, and more specifically to carbon-plus-nitrogen austenitic alloys that are interstitially strengthened, apparatus comprising these novel alloys, and methods of making and using same.
2. Related Art
The art of fabricating corrosion resistant ferrous alloys (including stainless steels and the so-called “high-nitrogen steels”) is well-documented (see Kamachi Mudali, U., Baldel Raj, “High Nitrogen Steels and Stainless Steels-Manufacturing, Properties and Applications”, Narosa Publishing House, ASM International, New Delhi (2004), hereinafter referred to as “Kamachi”). The use of nitrogen (N) as an alloying element is also well reported; however nitrogen (N) in high contents (or concentrations; in this document the two words are used interchangeably with no distinctions) is still not common, and when utilized nitrogen (N) has been restricted to alloys with low carbon contents. Nitrogen (N) yet continues to be of interest because of its abundance and low price (nitrogen gas, N2, constitutes about 80% of our atmosphere) and the fact that it serves as partial substitute to metallic alloying elements such as nickel (Ni) or chromium (Cr). Indeed, like nickel (Ni), nitrogen (N) is an austenite (γ) stabilizer (i.e. it stabilizes the austenite, the γ and FCC phase of iron), and like chromium (Cr), nitrogen (N) improves corrosion resistance immensely regardless of the fact that chromium (Cr) is a ferrite stabilizer (i.e. it promotes ferrite, the BCC α and δ phases of iron). In contrast with numerous grades of stainless steels, the high-nitrogen steels are essentially commercially unavailable. Of the various types of ferrous alloys, this invention relates exclusively to austenitic alloys (i.e. alloys that contains austenite, γ, as the predominant phase), and does thus not include either ferritic or martensitic alloys; two types of ferrous microstructures that are inherently limited by their cracking susceptibility in hydrogen-containing environments, including the sour environments of many oilfields. Specifically, included in this invention are alloys that are made fully austenitic largely due to interstitial carbon (C) and nitrogen (N), and alloys wherein other phases may coexist with the austenite phase but only in minor proportions (e.g. less than 5 wt. %). These minor phases may include other ferrous phases such as ferrite (α), martensite (with no restrictions to the various types of martensite), intermetallic phases or compounds of metals and nitrogen (N), carbon (C), or other non-metallic element, even though these phases will generally reduce the overall performance of the alloy in corrosive environments; that is its corrosion resistance. In this document, an alloy will be considered corrosion resistant when it resist the formation of pits and crevices, as well as the formation of cracks, as assisted by the presence of tensile stresses and a aggressive environment, in particular a sour, or H2S-containing environment, and/or a halide containing environment (as in brine or seawater).
U.S. Pat. No. 6,168,755 B1, (Biancaniello, et al.), discloses that a “high-nitrogen stainless steel” may be defined as a stainless steel having a nitrogen (N) content of at least 0.3 wt. %. In the presence of such or higher contents of nitrogen (N), the “high-nitrogen steels” have little or no carbon (C) because carbon (C), chromium (Cr), and other alloying elements commonly interact with carbon (C) to form in coexistence with the ferrous phases a variety of new phases, commonly lowering alloy corrosion resistance. Biancaniello, et al., after mentioning that certain patents (such as U.S. Pat. No. 5,480,609 by Dupoiron, et al.) teach to avoid nitrogen (N) over 0.8 wt. %, describe a high-nitrogen stainless steel having 0.8 to 0.97 wt. % nitrogen (N) with absolutely no carbon (C). U.S. Pat. No. 5,841,046 (Rhodes, et al.) describes a high-nitrogen stainless steel having between 0.8 and 1.1 wt. % nitrogen (N), and also clearly specifies that the new alloy requires solution annealing and water quenching in order to avoid chromium nitride precipitation as well as sigma (σ) phase; i.e. two phases that accelerate corrosion. EP 16261001A1 (Daido) discloses a high-nitrogen austenitic stainless steel having 0.8 wt. % to 1.5 wt. % nitrogen (N), but is restricted to 0.2 wt. % carbon (C), also to prevent the formation of harmful phases in corrosive environments.
Clearly prior art has been to restrict carbon (C) content to avoid or carefully control carbides, nitrides, carbo-nitrides, sigma (σ), Chi (χ) phases, or other intermetallic and deleterious phases, especially (but not restrictively) along grain boundaries. The tight control in the contents of these phases is crucial for the alloys to exhibit adequate corrosion resistance as well as good ductility and toughness in service conditions. Table 1 presents a summary list including a great many commercial austenitic stainless steels, among which many have found oilfield applications. In addition to being non-magnetic (paramagnetic), these alloys are all to some extents corrosion resistant, including resistant to environmentally-assisted cracking; i.e. hydrogen and sulfide stress cracking, stress-corrosion cracking, corrosion fatigue, etc (elsewhere, such alloys are often referred as CRAs or corrosion-resistant alloys). Paramagnetism and resistance to embrittlement by hydrogen (H), as promoted by dissolved hydrogen sulfides (H2S) in oil and gas fields, are largely promoted by the fact that alloys of this invention are austenitic, as opposed to ferritic or martensitic. Also shown in Table 1 for these alloys are UNS numbers (designations), chemical compositions, Pitting Resistance Equivalent (PRE) numbers (an index characterizing resistance to pitting corrosion; the higher the PRE is the more corrosion resistant is the alloy), and key mechanical properties. It may be seen for all these alloys that carbon (C) content is tightly controlled to never exceed 0.03 wt %. Likewise, content in nitrogen (N) is frequently less than 0.3 wt. %, as opposed to the high-nitrogen steels for which nitrogen content exceeds 0.3 wt. %. Except with rare exceptions, note that chromium (Cr) is consistently between 16 wt. % and 28 wt. %, nickel (Ni) ranges between 10 wt. % and 46 wt. %, molybdenum (Mo) is always present with a minimum of 0.5 wt. % increased up to 4.0 wt %, whereas manganese (Mn)—a strong austenite (γ) stabilizer—is not utilized. It is also seen that the chromium-rich and molybdenum-rich austenitic alloys have greater PRE (up to 54) and are thus more corrosion resistant, but also pricier, as shown by the last column of Table 1, and largely explained by the presence of nickel (Mo) and molybdenum (Mo). In stark contrast with the alloys of this invention is also the fact that the minimum yield strength is consistently lesser than 90 MPa (˜12 ksi) for most alloys; the exceptions being alloys that falls under the “high-nitrogen steel” category. Differently, the tensile elongation that measures ductility and thus indirectly toughness is relatively high and between 30 and 40 percent regardless of the alloys; a characteristic that makes austenitic alloys advantageous for countless applications, including artic usage where for instance brittle fracture would likely occur in ferritic or martensitic steels. Of all the properties of the commercial alloys of Table 1, their strength is often insufficient for downhole applications and thus constitutes a major disadvantage that prevents them from rivaling the nickel alloys used today in downhole applications, and, when their strength is adequate, these alloys are considerably pricy, thus establishing another limit to their use. However, in part related to their excellent toughness, the austenitic alloys are promising for use in oil and gas applications, especially in sour environments, whereas the martensitic steels are inherently limited by their poor resistance against hydrogen embrittlement (including sulfide stress cracking). FIG. 1 is a histogram chart for the major alloys currently used in oilfield subsurface applications (including completion equipment) showing price estimates per pounds (normalized to that of carbon steels) along with the alloy recommended tensile strengths. While all these alloys may exist in higher strength grades through cold working (work hardening), heat-treatments, or both, note that alloy strength is limited as shown in FIG. 1, largely to comply with NACE MR0175/ISO15153 standards and thus be acceptable by the industry.
In ferrous alloys, the simultaneous use of carbon (C) and nitrogen (N) has been reported in published articles by Rawers and Gavriljuk (Rawers) on iron (Fe) and on Fe-15 wt. % Cr-15 wt. % Mn alloys. As part of this invention, a similar contribution from carbon (C) and nitrogen (N) is proposed for different and more complex alloys that have the advantages of having low-raw material costs, high resistance in corrosive environments—including resistant to sulfide stress cracking (SSC)—, high strengths (>700 MPa; ˜100 ksi), and high toughness values (>40J; ˜30 ft. lb). Today, there are no carbon-plus-nitrogen commercial alloys available, whether they are stainless or not, and only one patent (to best of our knowledge) on the subject has been found, but for different alloy compositions and entirely-different applications, in stark contrast with the countless patents that have been granted for steels and stainless steels for instance. When compared to the commercial alloys of Table 1, the novel carbon-plus-nitrogen alloys of this invention simply offer new and improved properties, nearly all superior to those listed in Table 1; properties that bring new oilfield applications for these relatively-low cost inventive alloys. Of great interest to downhole applications is the use of these novel alloys in sour conditions, as well as their use at greater depths (e.g. HPHT wells), where today conventional austenitic steels would not be employed.
A number of scientific publications (e.g. journal articles, patents, standards) will serve as references to this document. They will be usually referred in this document by the first author's name or owning company: e.g. Rawers, J. C., “Characterizing alloy additions to carbon high-nitrogen steel”, Proceedings of the Institution of Mechanical Engineers, Journal of Materials: Design and Applications, Vol. 218, No. 13, pp. 239-246 (August 2004) (Rawers); Gavriljuk, et al., “Nitrogen and carbon in austenitic and martensitic steels: atomic interactions and structural stability”, Materials Science Forum, Vol. 426-432, Part 2, pp. 943950 (2003) (Gavriljuk, et al.); Balanyuk, et al., “Mössbauer study and thermodynamic modeling of Fe—C—N alloy”, Acta Materialia, Vol. 48, No. 15, pp. 3813-3821 (September 2000) (Balanyuk, et al.); Saller, et al., US20050145308 A1 (Saller, et al.); Hamano, et al., US20060034724 A1 (Hamano, et al.); ALLVAC Ltd., et al., EP1051529 B1 (ALLVAC); Radon, US 2004/0258554 A1 (Radon), Jargelius-Pettersson, R. F., “Application of the pitting resistance equivalent concept to some highly alloyed austenitic stainless steels”, Corrosion (USA), Vol. 54, No. 2, pp. 162-168. (February 1998) (Jargelius-Pettersson); “Petroleum and natural gas industries—Materials for use in H2S-containing Environments in oil and gas production”, NACE MR0175/ISO 15156 International Standard; Kovach, C. W., “High-Performance Stainless Steels”, Technical report to the Nickel Development Institute.
Published U.S. patent application no. 20050145308 (Saller, et al.) discloses steels comprising, among other ingredients, from 0 wt. % to about 0.35 wt. % carbon (C), and from about 0.35 wt. % to about 1.05 wt. % nitrogen (N). The authors note that hot working a cast piece in one or more steps, an optional subsequent solution annealing of the semi-finished product, and forming at a temperature below the recrystallization temperature (preferably below about 600° C. or 1140° F.) produces a steel essentially free of nitrides, carbides, carbo-nitrides, apparently affording a high fatigue strength under reversed stresses of the same. Being substantially free of nitrogenous and carbide precipitations, parts made of steels may be produced (according to this publication) with both superior mechanical properties and greater stress-corrosion cracking and pitting corrosion resistances. The austenitic alloys of this publication may be employed in principle for drilling string components, such as drill rods for oilfield technology.
Articles made of hot-worked and cold-worked austenitic alloys with up to 0.12 wt. % carbon (C), 0.20 wt. % to 1.00 wt. % silicon (Si), 17.5 wt. % to 20.0 wt. % manganese (Mn), up to 0.05 wt. % phosphorus (P), up to 0.015 wt. % sulfur (S), 17.0 wt. % to 20.0 wt. % chromium (Cr), up to 5 wt. % molybdenum (Mo), up to 3.0 wt. % nickel (Ni), and from 0.8 wt. % to 1.2 wt. % nitrogen (N) are known from DE 39 40 438 C1. However, as noted by some of the same inventors in DE 196 07 828 A1, these articles have modest fatigue strength—at best 375 MPa (55 ksi)—and this fatigue strength is significantly lower in an aggressive environment such as saline environments.
Another austenitic alloy is known from DE 196 07 828 A1, mentioned above. According to this document, articles are proposed for the offshore industry which are made of an austenitic alloy with 0.1 wt. % carbon (C), 8 wt. % to 15 wt. % manganese (Mn), 13 wt. % to 28 wt. % chromium (Cr), 2.5 wt. % to 6 wt. % molybdenum (Mo), 0 wt. % to 5 wt. % nickel (Ni) and 0.55 wt. % to 1.1 wt. % nitrogen (N). Such articles are reported to have high mechanical properties, particularly a higher fatigue strength under reversed stresses than articles according to DE 39 40 438 C1. However, one disadvantage thereof is a low nitrogen (N) solubility that is attributable to the alloy composition, which is why melting and solidification have to be carried out under pressure, or still more burdensome powder metallurgical production methods must be utilized.
An austenitic alloy which results in articles with low magnetic permeability and good mechanical properties with melting at atmospheric pressure is described in AT 407 882 B. Such an alloy has in particular relatively high yield strength, a high tensile strength, and high fatigue strength under reversed stresses. Alloys according to AT 407 882 B are expediently hot worked and subjected to a second forming at temperatures of 350° C. to approximately 600° C. The alloys are said to be suitable for the production of drill rods which also adequately take into account the high demands with respect to static and dynamic loading capacity over long operating periods within the scope of drill use in oilfield technology.
Published U.S. Pat. App. No. 20050047952 (ALLVAC LTD.) discloses an alloy claimed to be non-magnetic, corrosion resistant, galling resistant, and high strength and suitable for use as non-magnetic components in directional drilling of oil and gas wells whose composition by weight includes: carbon (C) up to 0.2 wt. %; silicon (Si) up to 1.0 wt. %; manganese (Mn) from 10.0 to 20.0 wt. %; chromium (Cr) from 13.5 to 18.0 wt. %; nickel (Ni) from 1.0 to 7.0 wt. %; molybdenum (Mo) from 1.5 to 4.0 wt. %; and nitrogen (N) from 0.2 to 0.4 wt. %, the composition satisfying the formulae: nickel equivalence (Nieq)+chromium equivalence (Creq) greater than 35; a formula of questionable meaning since nickel and chromium have widely different effects, in particular chromium (Cr) is ferrite stabilizer while nickel (Ni) is an austenite (γ) stabilizer.
The first report of the benefits carbon (C) and nitrogen (N) could bring if used in combination may probably be found in articles co-authored by Gavriljuk et al., in particular the article referred in this patent as Balanyuk, et al. In the referred article, Mössbauer spectroscopy and Monte Carlo computer simulation were combined to understand the reason for the solid-solution stability of iron (Fe) alloyed with 0.93 wt. % carbon (C) and 0.91 wt. % nitrogen (N). Interstitial concentrations in austenite (γ) and ferrite (α) were determined on the basis of X-ray diffraction measurements of the lattice dilatation. The hyperfine structure of Mössbauer spectra was analyzed to identify different atomic configurations in solid solutions and determine their fractions. Thereafter Monte Carlo simulation of the interstitial distribution in ferritic and austenitic solid solutions was performed, and values of the interstitial-interstitial interaction energies were obtained for the first and second coordination spheres in austenite (γ) and the first to the fourth coordination spheres in ferrite (α). Simulations showed that in both austenitic and ferritic phases the interaction of interstitial atoms is characterized by a strong repulsion within the first two coordination spheres. Experimental data and simulated interstitial distributions are consistent and complementary, and Balanyuk, et al. concluded that the absence of interstitial clusters prevents carbide and nitride precipitates and causes the higher thermodynamic stability of Fe—C—N solid solutions as compared with Fe—C and Fe—N ones.
Of all patents, only one (US published patent application no. 20040258554 A1 by Radon)—discloses alloys closer to the austenitic alloys of this invention, but the authors did not appear to have recognized the critical role played by the combination of carbon-plus-nitrogen in solid solution. Furthermore, unlike the austenitic alloys of the present invention, 31 wt. % to about 48 wt. % chromium (Cr) were used by Radon, while nitrogen (N) and carbon (N) contents were slightly more restricted; carbon (C) was between 0.3 wt. % to 2.5 wt. % (thus higher than in this invention) while nitrogen (N) was between 0.01 wt. % to 0.7 wt. %. Though the carbon (C) and nitrogen (N) contents were occasionally similar to those found in this patent, the author always uses more chromium (Cr) than in the alloys of the present invention, and the problem to be solved and the foreseen applications were extremely different.
As described in this document, corrosion is a complex type of damage and the exact behavior of various alloys cannot be precisely predicted in different oilfield environments. The important criteria with respect to corrosion in oil and gas environments are temperature, and concentrations of sulfides (H2S), carbon dioxides (CO2) and halides (e.g. chlorides). The presence of water and its chemical composition also plays an important role. In either designing or selecting alloys for oil and gas applications, primary consideration are given to cracking; including sulfide stress cracking at low temperatures as well as stress-corrosion cracking generally at higher temperatures. All cracking and weight loss, pitting and crevice corrosion are reduced with austenitic alloys of high PRE and MARC numbers. In addition to providing strengths, the carbon-plus-nitrogen austenitic alloys of the present invention, thanks to their high PRE and MARC numbers, are predicted to outperform many currently known alloys and at lower cost estimates. Tables 1 and 2 show the PRE (Pitting Resistance Equivalent) and MARC (Measure of Alloying for Corrosion Resistance) numbers of commercial austenitic alloys. PRE number ranges between 22 and 54, with corresponding MARC numbers as high as 23. These values are in stark contrast with the inventive alloys described in this document. PRE and MARC numbers are defined later in this document.
For oil and gas applications, ferrous and austenitic alloys which simultaneously use carbon (C) and nitrogen (N) in interstitial solid solution, are of great interest, in particular if they have also a high corrosion resistance in a multitude of aggressive environments and possess good mechanical properties, in particular a high 0.2% yield strength (YS) and a high tensile strength (TS). In addition, if these alloys can be melted at atmospheric pressure (and if not, with manageable over pressuring; e.g. 2-3 atmospheres), as it is indented for most of the disclosed compositions, their manufacturing-ability and cost would further guarantee their future industrial acceptance.
TABLE 1Chemical compositions, PRE numbers (corrosion resistance), mechanical properties and price estimate for anumber of commercial stainless steels (Kovach).UNSNameNumberCNCrNiMoCuOtherType 316LS316030.030.1016.0-18.010.0-14.02.0-3.0——Type 317LS317030.030.1018.0-20.011.0-15.03.0-4.0——Alloy 20N080200.07—19.0-21.032.0-38.02.0-3.03.00-4.00(Cb + Ta): 8 × C − 1.00Alloy 825N088250.05—19.5-23.538.0-46.02.5-3.51.50-3.50Al: 0.2 max, Tl: 0.6-1.2317LNS317530.030.10-0.2218.0-20.011.0-15.03.0-4.0——2600.030.16-0.2418.5-21.513.5-16.52.5-3.51.00-2.00—317LMS317250.030.1018.0-20.013.2-17.54.0-5.0——317LMNS317260.030.10-0.2017.0-20.013.5-17.54.0-5.0——NAS 204X0.04—25.025.02.75—Nb: 10 × C310MoLNS310500.030.10-0.1624.0-26.021.0-23.02.0-3.0—Sl: 0.50 max700N087000.04—19.0-23.024.0-26.04.3-5.0—Nb: 8 × C − 0.40904LN089040.02—19.0-23.023.0-28.04.0-5.01.00-2.00—904LN0.020.04-0.1519.9-21.024.0-26.04.0-5.01.00-2.0020Mo-4N080240.03—22.5-25.035.0-40.03.5-5.00.50-1.50—20 ModN083200.05—21.0-23.025.0-27.04.0-6.0—Tl: 4 × C minAlloy 28N080280.02—26.0-28.029.5-32.53.0-4.00.60-1.40—20Mo-6N080260.030.10-0.1622.0-26.033.0-37.05.0-6.72.00-4.00—25-6M0N089250.020.10-0.2019.0-21.024.0-26.06.0-7.50.8-1.5—1925hMo254N0.030.2023.025.05.50——25-6M0N089260.020.15-0.2519.0-21.024.0-26.06.0-7.00.50-1.50—1925hMoSB8N089320.020.17-0.2524.0-26.024.0-26.04.7-5.71.0-2.0—254 SM0S312540.020.18-0.2219.5-20.517.5-18.56.0-6.50.50-1.00—AL-6XNN083670.030.18-0.2520.0-22.023.5-25.56.0-7.00.75—YUS 1700.030.25-0.4023.0-26.012.0-16.00.50-1.20——2419 MoN0.030.30-0.5023.0-25.016.0-18.03.5-4.50.30-1.00Mn: 5.5-6.54565SS345650.030.40-0.6023.0-25.016.0-18.03.5-5.0—Mn: 3.5-6.5B66S312660.0300.35-0.6023.0-25.021.0-24.05.0-7.00.50-3.00W: 1.0-3.0Mn: 2.00-4.003127 hMoN080310.020.15-0.2526.0-28.030.0-32.06.0-7.01.00-1.40—654 SM0S326540.020.45-0.5524.0-26.021.0-23.07.0-8.00.30-0.60Mn: 2.0-4.0Cu: 0.3-0.6TensileYieldRaw metalStrengthStrengthHardnessprice*(minimum)(minimum)(maximum)(2005NamePREksiMPaksiMPaElongation %BrinellHRB$/lb)Type 316L23704852517040217962.1Type 317L28755153020540217962.5Alloy 2026805513524130217963.7Alloy 82528855863524130——4.3317LN30805503524040217962.526029805504027535217—2.5317LM31755153020540217963.0317LMN32805503524040223973.0NAS 204X34735003021035187903.2310MoLN32805503524030217962.970033805503524030—903.7904L32714903122035——3.7904LN343.720Mo-434805513524130217964.520 Mod34755172819335—953.9Alloy 2836735003121440——3.920Mo-640805513525130217964.925-6M0—946504329535——4.41925hMo254N41946504330035217964.025-6M0414.31925hMoSB842795503725035——4.0254 SM042946504430035223973.8AL-6XN431006904531030240—4.3YUS 170291006904330035217971.92419 MoN391208206746030——3.14565S411158006142035——3.1B66454.13127 hMo48946504027640——4.9654 SM0541097406242535250—4.5*Raw material prices were estimated using 2005 average metal prices and a lever rule; i.e. from the percent of each alloying elements. Processing costs are not included in the estimated prices. Prices are subject to the laws of demand and supply and may be very different from those shown in this table.
TABLE 2Representative corrosion characteristics and applications for high-performance stainless steels (Kovach).PREMARCDESCRIPTIONAPPLICATIONS (OUTSIDE OILFIELDS)AUSTENITIC ALLOYS22-288 maxResistance to mid-concentration sulphuric and other strong, mildlyProcess equipment handling sulphuric acid solutions; condensersreducing or oxidizing acids. Resistance to stress corrosion andand coolers handling acid-chloride condensates where stresspitting (at high PRE number)corrosion is a problem30-32Good resistance to mildly acidic, moderate chloridePiping operating under mild conditions, equipment requiringaqueous environments while providing a moderateimproved performance compared to Type 316strength advantage32-3613-15Good general and stress corrosion resistance in strong acidsGeneral process equipmentat moderate temperatures and in organic acids at high temperatures40-4314-21Very good chloride pitting and stress corrosion resistance;Process equipment for all but strong reducing and hot sulphuricresists seawater and many saline acidic waters, and many acids andacids; piping and heat exchangers handling ambient seawatercaustics; provides a substantial strength advantage29-41Very high strength and good general corrosion and pittingWhere high strength is importantresistance45-5413-23Very high strength with excellent chloride pitting and stressProcess equipment for all but strong reducing and hot sulphuriccorrosion resistance, resists warm seawater and high chloride,acids; piping and heat exchangers/evaporators handling hotacidic and oxidizing waters and brines; excellent resistance to aseawater and brineswide variety of acids and causticsFERRITIC ALLOYS278Excellent chloride stress corrosion cracking resistance, goodHeat exchanger tubing handling fresh water, organic acidresistance to pitting; excellent resistance to hot organiccondensers, caustic evaporator tubingacids and caustics34-40 4-14Resistant to pitting and crevice corrosion in ambient temperatureSeawater-cooled condenser tubing; heat exchanger tubingseawater; good stress corrosion resistance in high temperaturehandling fresh and brackish water and organic acidswater; good strengthDUPLEX ALLOYS228 maxGood stress corrosion resistance in cooling waters and underEquipment handling water, foods, and pharmaceuticals whereevaporative conditions; high strengthbetter strength or stress corrosion resistance is needed comparedto Type 30430-34 5-12Good pitting and stress corrosion resistance; good resistance toPressure vessels, piping, pumps and valves where strength andoxidizing acids and caustics; high strengthweight are factors along with resistance to stress corrosion andfatigue32-39 7-15Very good pitting and stress corrosion resistance, goodWhere better pitting and crevice corrosion resistance is neededresistance to mildly reducing and oxidizing acids andcompared to the D-2 alloyscaustics; high strength36-3810-14Resistance to seawater pitting and crevice corrosion; very goodPumps, valves, and high pressure piping and pressure tubingstress corrosion resistance; good resistance to mildly reducinghandling seawater or chloride containing watersacids and oxidizing acids and caustics; high strength